.TH std::uninitialized_copy 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::uninitialized_copy \- std::uninitialized_copy

.SH Synopsis
   Defined in header <memory>
   template< class InputIt, class NoThrowForwardIt >

   NoThrowForwardIt uninitialized_copy( InputIt first, InputIt last,  \fB(1)\fP

                                        NoThrowForwardIt d_first );
   template< class ExecutionPolicy, class ForwardIt, class
   NoThrowForwardIt >

   NoThrowForwardIt uninitialized_copy( ExecutionPolicy&& policy,     \fB(2)\fP \fI(since C++17)\fP
                                        ForwardIt first, ForwardIt
   last,

                                        NoThrowForwardIt d_first );

   1) Copies elements from the range [first, last) to an uninitialized memory area
   beginning at d_first as if by for (; first != last; ++d_first, (void) ++first)
       ::new (/* VOIDIFY */(*d_first))
           typename std::iterator_traits<NoThrowForwardIt>::value_type(*first);
   where /* VOIDIFY */(e) is:

   static_cast<void*>(&e)                \fI(until C++11)\fP
   static_cast<void*>(std::addressof(e)) \fI(since C++11)\fP

   If an exception is thrown during the initialization, the objects already constructed
   are destroyed in an unspecified order.

   If d_first + [0, std::distance(first, last)) overlaps with             \fI(since C++20)\fP
   [first, last), the behavior is undefined.

   2) Same as \fB(1)\fP, but executed according to policy. This overload participates in
   overload resolution only if

   std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.        (until
                                                                             C++20)
   std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since
                                                                             C++20)

.SH Parameters

   first, last           -        the range of the elements to copy
   d_first               -        the beginning of the destination range
   policy                -        the execution policy to use. See execution policy for
                                  details.
.SH Type requirements
   -
   InputIt must meet the requirements of LegacyInputIterator.
   -
   ForwardIt must meet the requirements of LegacyForwardIterator.
   -
   NoThrowForwardIt must meet the requirements of LegacyForwardIterator.
   -
   No increment, assignment, comparison, or indirection through valid instances of
   NoThrowForwardIt may throw exceptions.
   Applying &* to a NoThrowForwardIt value must yield a pointer to its value type.
   \fI(until C++11)\fP

.SH Return value

   Iterator to the element past the last element copied.

.SH Complexity

   Linear in the distance between first and last.

.SH Exceptions

   The overload with a template parameter named ExecutionPolicy reports errors as
   follows:

     * If execution of a function invoked as part of the algorithm throws an exception
       and ExecutionPolicy is one of the standard policies, std::terminate is called.
       For any other ExecutionPolicy, the behavior is implementation-defined.
     * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

.SH Possible implementation

template<class InputIt, class NoThrowForwardIt>
NoThrowForwardIt uninitialized_copy(InputIt first, InputIt last, NoThrowForwardIt d_first)
{
    using T = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = d_first;
    try
    {
        for (; first != last; ++first, (void) ++current)
            ::new (static_cast<void*>(std::addressof(*current))) T(*first);
        return current;
    }
    catch (...)
    {
        for (; d_first != current; ++d_first)
            d_first->~T();
        throw;
    }
}

.SH Example


// Run this code

 #include <cstdlib>
 #include <iostream>
 #include <memory>
 #include <string>

 int main()
 {
     const char *v[] = {"This", "is", "an", "example"};

     auto sz = std::size(v);

     if (void *pbuf = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz))
     {
         try
         {
             auto first = static_cast<std::string*>(pbuf);
             auto last = std::uninitialized_copy(std::begin(v), std::end(v), first);

             for (auto it = first; it != last; ++it)
                 std::cout << *it << '_';
             std::cout << '\\n';

             std::destroy(first, last);
         }
         catch (...) {}
         std::free(pbuf);
     }
 }

.SH Output:

 This_is_an_example_

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

      DR    Applied to          Behavior as published              Correct behavior
                       given T as the value type of
   LWG 866  C++98      NoThrowForwardIt, if                    uses global replacement-
                       T::operator new exists, the program     new instead
                       might be ill-formed
                       the effect description used a for loop
                       with the iteration                      discards the value
   LWG 2133 C++98      expression ++d_first, ++first, which    of one operand
                       results                                 to disable that ADL
                       in an argument-dependent lookup of
                       operator,
   LWG 2433 C++11      this algorithm might be hijacked by     uses std::addressof
                       overloaded operator&
   LWG 3870 C++20      this algorithm might create objects on  kept disallowed
                       a const storage

.SH See also

   uninitialized_copy_n       copies a number of objects to an uninitialized area of
   \fI(C++11)\fP                    memory
                              \fI(function template)\fP
   ranges::uninitialized_copy copies a range of objects to an uninitialized area of
   (C++20)                    memory
                              (niebloid)
